Nitric oxide diffusion in membranes determined by fluorescence quenching

Area of Science:

• Biophysics
• Membrane Transport
• Chemical Kinetics

Background:

• Nitric oxide (NO) plays crucial roles in biological systems, necessitating understanding its membrane transport.
• Fluorescence quenching is a sensitive method for studying molecular interactions and diffusion.

Purpose of the Study:

• To determine the apparent diffusion coefficients of nitric oxide (NO) in artificial (liposomes) and biological (erythrocyte) membranes.
• To compare the diffusional behavior of NO with oxygen (O2) in these membranes.
• To investigate the influence of membrane depth on gas solubility and diffusion.

Main Methods:

• Utilized fluorescence quenching of pyrene derivatives by NO to quantify quenching constants.
• Employed Stern-Volmer plots to determine apparent second-order quenching constants.
• Incorporated methyl- and undecylpyrene derivatives into liposomes and erythrocyte membranes.
• Calculated diffusion coefficients from quenching constants and compared NO and O2 diffusion.

Main Results:

• NO and O2 exhibit similar diffusion behavior, attributed to structural similarities.
• O2 diffusion is approximately twice as fast as NO diffusion in liposomes and erythrocyte ghosts.
• Gas solubility increases towards the membrane core, as indicated by higher quenching constants for undecylpyrene derivatives.

Conclusions:

• NO diffusion coefficients in membranes range from 0.4-1.3 x 10^-5 cm^2/s at 20°C.
• Differences in diffusion rates are linked to the higher lipophilicity of O2 compared to NO.
• Findings provide insights into NO's membrane permeability and interaction dynamics within lipid bilayers.